Geology of Middle to Upper Ordovician Sebree Trough Northwest of Cincinnati Arch, Ohio, Indiana, and Kentucky

Stig M. Bergstrom, Charles E. Mitchell

The Sebree trough, which has attracted interest in hydrocarbon exploration, is a broadly linear, northeast-oriented, troughlike structure northwest of the Cincinnati arch that can be traced from western Ohio through southeastern Indiana to western Kentucky. The post-Black River, pre-upper Kope succession of the Sebree trough differs markedly in lithology from that of the Cincinnati arch, in which limestones dominate (Trenton and Lexington Limestones), in that it consists mainly of dark-brown to grayish shales ("Utica" of drillers). The Sebree trough is not displayed by the isopach pattern of the Black River, nor by that of post-Kope strata. Apparently, this feature is restricted to the upper Middle and lower Upper Ordovician. Absence of biostratigraphic control in the "Ut ca," as well as poor well control in the area bordering the Cincinnati arch carbonate region, made previous interpretations of the stratigraphic relations between the "Utica" and the Lexington-Trenton hypothetical. Recent detailed study of two cores from eastern Indiana and one from western Ohio led to the discovery of a succession of biostratigraphically diagnostic graptolites in the "Utica" that can be tied into that of the C. spiniferus and C. pygmaeus zones in the Utica Shale of New York. The new evidence shows that at least the major parts of the "Utica" and the Lexington-Trenton are correlatives, although these units are developed in quite different facies.

AAPG Search and Discovery Article #91041©1987 AAPG Eastern Section Meeting, Columbus, Ohio, October 7-10, 1987.